Ultra-high-intensity and ultra-fast laser pulses from laser amplifiers are essential requirements for high energy physics and National defense applications. Transverse parasitic lasing has however been up until now a bottleneck in Petawatt (1015 watts) level Ti doped sapphire laser systems with large aperture gain crystals. A larger pumping areas leads to higher transverse gain experienced by radially-emitted spontaneous emission. If this gain becomes higher than the Fresnel losses experienced at the edge of the gain crystal, parasitic oscillations inside this transverse laser cavity will arise, depleting the population inversion and preventing desired amplifying action of the longitudinally-incident seed pulse. Besides, the thermal load from the higher pumping powers can degrade laser quality from an index gradient or lead to catastrophic damage to the gain crystals. Thus, generally either the power or repetition rate has to be limited, and special cryogenic cooling has to be applied.
The conventional procedure against parasitic laser generation is to reduce the reflectivity of the side wall of the gain crystals by coating them with a refractive index-matched absorptive polymer layer or liquids. These approaches however have various issues. For example, the absorptive polymer generally only has a matched index at one wavelength point and it has low thermal conductivity and different thermal expansion than the gain crystal.